The main communication channel that the Server uses to communicate with ACC Controllers is Ethernet. Each controller sends and receives messages to and from the Server and the hardware devices that monitor the system. All the components used in the SiPass integrated system are ultimately connected to the Server.

There is virtually no limit to the total number of controllers that can be connected. Various networking options (LAN/WAN/PSTN) can expand the system to include buildings and locations all over the world. AscoServer is the executable used by the SiPass server that acts as the gateway to remotely access SiPass resources on port 4343. The Ethernet Bus library connects the Server to the advanced Central Controllers (ACC) and allows communication between the Server and defined devices and points. Ethernet communication means that AscoServer doesn t need a dedicated Bus, because both Windows and the ACC understand the TCP/IP protocol used to send and receive messages over Ethernet networks.

After creating an I/O completion port with an existing file descriptor, the server begins listening for IOCP messages on that port. When the server receives an IOCP message, it creates substructure elements that are copied into shared memory between threads.Due to insufficient sanity checking when manipulating an IOCP message, it is possible to alter the behavior of message parsing, allowing another IOCP message to subvert the listener of IOCP messages, leading to export of a write-n primitive.

This allows an attacker to write arbitrary data within the application, leading to remote code execution. Since the application spawns multiple threads for handling Ethernet connections,one approach for exploiting the vulnerability would be to overwrite a pointer to the first exception handler in any of the Thread Environment Block (TEB) structures and seize control of the exception-handling thread after an access violation. Even though Thread data blocks are randomized, addresses are stable because multiple identical threads are created.